1. Field of the Invention
The present invention relates to a battery module and a method for manufacturing the battery module consisting of a plurality of cells connected by welding, each cell comprising a group of electrodes having a positive electrode and a negative electrode laminated via a separator and an electrolytic solution, which are contained and hermetically sealed within a metallic can serving as a terminal of one electrode.
2. Description of the Related Art
Generally, in the alkaline batteries such as a nickel-hydride battery or a nickel-cadmium battery, a positive electrode and a negative electrode with a separator interposed are wound like a vortex, a collector is connected to the end of the positive electrode or negative electrode to form an electrode assembly, and this electrode assembly is contained within a metallic case. Thereafter, a lead part extending from the collector is welded to a sealing member, and the sealing member is attached via an insulating gasket to an opening portion of the battery case, whereby an alkaline battery is hermetically sealed. When such alkaline battery is employed in the electric tools or electric vehicles, owing to the requirement for a high output, it is common use that a battery module is made by connecting a plurality of cells in series.
Such battery module is produced in such a way as to weld one end of a lead plate 85 to a positive electrode cap 82 provided as a positive electrode terminal on a sealing plate 81 of a cell 80b, and the other end of the lead plate 85 to a bottom portion 84 of a metallic can 83 of a cell 80a, with a central part of the lead plate 85 being bent like U character, whereby a plurality of cells 80a, 80b are connected in series, as shown in FIG. 15.
By the way, if the plurality of cells 80a, 80b connected via the lead plate 85 bent like U character are discharged, a discharge current flows through the lead plate 85. Therefore, the voltage drop increases, as the lead plate 85 is longer and thinner. This voltage drop is not so problematical when the discharge current is small, but when the battery module is employed in the uses where a large current flows such as the power tools or electric vehicles, there is the problem that the operation voltage may decrease due to the voltage drop.
Therefore, a method was conceived in which the cells were connected directly by soldering the opposite terminals of the cells without the use of the lead plate. However, there was the problem that the soldering had a weaker strength of the connected portion than the welding, and was difficult to effect the connection securely. Also, there was another problem that it was troublesome or poor in working efficiency to solder the opposite electrodes of the cells.
Thus, as a result of various experiments, the present applicants have developed an epochal method of welding directly the adjacent terminals of the cells bypassing a welding current in a direction of charging or discharging the cells. This method is one in which a plurality of cells 90a, 90b are contained within a holding barrel, not shown, and aligned in one row, then one welding electrode 96 being placed on a positive electrode cap 92 of a cell at an uppermost end thereof, and the other welding electrode 97 being placed on a bottom 94 of a metallic can 93 of a cell at a lowermost end thereof, as shown in FIG. 16.
Thereafter, a voltage is applied between the welding electrodes 96, 97 which are subjected to a pressure to conduct a large pulse current. Thereby, a contact part between the bottom 94 of the metallic can 93 of a cell 90a and the positive electrode cap 92 of a cell 90b is molten and welded.
Thereby, the adjacent terminals of the cell are directly welded together, whereby a voltage drop across this welded portion decreases, so that the battery module has an improved operation voltage.
However, if a plurality of cells are aligned in one row, a pair of welding electrodes are disposed at both ends thereof, a voltage is applied between the pair of welding electrodes which are subjected to pressure to conduct a large pulse current to weld the contact part between the bottom of the metallic can of one cell and the positive electrode cap of the other cell, as described above, an excessive pressure may be directly exerted to the positive electrode cap when the pair of welding electrodes are pressurized. In this case, there was the problem that when the excessive pressure was applied to the positive electrode cap, the positive electrode cap might be compressed or deformed.
Since a pressure valve was disposed within the positive electrode cap, there was the problem that the pressure valve might be operated abnormally if the positive electrode cap was compressed or deformed.
The present invention has been achieved to solve the above-mentioned problems, and its objective is to provide a battery module of a structure in which a number of cells are welded without damaging a cap portion containing a pressure valve and causing a welding failure.
In order to achieve the above-mentioned objective, according to the present invention, a battery module consisting of a plurality of cells electrically connected, each cell comprising a case (metallic can) serving as a terminal of one electrode and containing a cell element with a positive electrode and a negative electrode disposed to sandwich an electrolyte, and a terminal of the other electrode isolated from said metallic can, said battery module comprising: a connecting member having at least one projection on each of said terminal sides between adjacent two terminals of said cells; wherein each of contact parts between said connecting member and said terminals of said cells are welded at said projection.
Preferably, said connecting member is welded at the contact part with the bottom of said can.
Preferably, said connecting member has an aperture in an area corresponding to said terminal, and is formed to surround said aperture.
Preferably, said connecting member is welded with said can at the bottom of said can, and is configured to reach a part of a lateral face along an outside periphery of said can, and cover the part of said lateral face.
Preferably, said connecting member is configured to reach a part of a lateral face along an outside periphery of said can, and is welded with said can at the lateral face of said can.
Namely, a battery module comprises a connecting member having an aperture at a position corresponding to a cap between a sealing member of one cell and a bottom of a can of the other cell, the aperture having a larger diameter than that of the cap, wherein a contact part between this connecting member and the sealing member of the one cell, as well as a contact part between this connecting member and the bottom of the can of the other cell are connected by welding respectively.
In this way, since the contact part between this connecting member and the sealing member of the one cell, as well as the contact part between this connecting member and the bottom of the can of the other cell are connected by welding respectively, the sealing member of the one cell and the bottom of the can of the other cell are electrically connected via the connecting member, whereby the connecting portion between the sealing member of the one cell and the bottom of the can of the other cell has a collecting path of a length equivalent to the height of the connecting member, namely, the length between the sealing member of the one cell and the bottom of the can of the other cell. Therefore, the voltage drop across the connecting portion decreases, resulting in a battery module with a high operation voltage.
If the sealing member of the one cell and the bottom of the can of the other cell are electrically connected via the connecting member having the aperture having a larger diameter than the cap at the position corresponding to the cap provided on the sealing member, the cap provided on the sealing member is not welded, so that the cap is not subjected to compression and deformation, or damage. Thereby, the battery module is produced without having effect on the operation pressure of a safety vent disposed within the cap.
And the connecting member is made of a conductive material, and comprises an annular base portion having its outer diameter smaller than an inner diameter of the opening portion of the can, a convex portion with bottom protruding upward or downward alternately from the base portion, and a projection projecting from the bottom of the convex portion, whereby owing to the convex portion with bottom protruding upward or downward alternately from the base portion, the annular connecting member can afford a resiliency between the sealing member of the one cell and the bottom of the can of the other cell.
Therefore, a welded portion between the projection projecting downward (or upward) and the sealing member of the one cell, as well as a welded portion between the projection projecting upward (or downward) and the bottom of the can of the other cell have the improved welding strength, whereby the voltage drop across the welded portion further decreases, resulting in the battery module with higher operation voltage. In this case, since the outer diameter of the annular base portion is smaller than the inner diameter of the opening portion of the can, the contact between the upper end part of the can of the one cell and the bottom of the can of the other cell can be prevented, resulting in the battery module that causes no welding failure.
Also, since the annular base portion is partially formed with a notch, the connecting member can be inserted between the cells, after the cells are aligned in one row. Therefore, the aligning operation of the cells is facilitated. The shape of the base portion may be polygonal, besides being annular. Since the connecting member comprises a first base portion curved or crooked along an outside periphery of the opening portion of the can, and a second base portion curved or crooked along an outside periphery of the opening portion of the can, the first base portion and the second base portion being spaced from each other with a cap interposed to form an aperture in the central part thereof, the inserting operation of the connecting member into the cells is further facilitated.
In the case where a battery module using such connecting member failed in the welded portion due to some accident, the welded portion on the bottom of the can is broken, if the thickness of the projection is greater than that of the bottom of the can, bringing about the danger that the electrolytic solution may leak. Hence, the thickness of the projection, as well as the thickness of the convex portion, are preferably smaller than that of the bottom of the can. If the thickness of the base portion is smaller than that of the bottom of the can, the connecting member has an increased resistance value, resulting in the problem that the output characteristic of the battery module decreases. The thickness of the base portion is preferably greater than that of the bottom of the can.
Also, since the annular connecting member has an annular insulating base plate having its outer diameter smaller than an inner diameter of the opening portion of the can, and a conductive ring integrally formed, the conductive ring being formed inside the base plate and jutted out vertically from the base plate, whereby the sealing member of the one cell and the bottom of the can of the other cell are connected via the conductive ring, so that the collecting path is equal to a height of the conductive ring. Therefore, the resistive voltage drop across the connecting portion decreases, resulting in a battery module with high operation voltage.
In this case, since the outer diameter of the annular insulating base plate is smaller than the inner diameter of the opening portion of the can, and the conductive ring is formed internally, the contact between the upper end part of the can of the one cell and the bottom of the can of the other cell can be securely prevented, resulting in a battery module causing no welding failure.
Also, the annular connecting member is made of a conductive material, and comprises a cylinder and a flange portion formed integrally with the bottom of the cylinder, with an insulating ring disposed around an outside periphery of the cylinder, the flange portion being welded to the sealing member of the one cell, an upper end of the cylinder being welded to the bottom of the can of the other cell. Therefore, the collecting path has a length equal to a height of the cylinder, whereby the voltage drop across the connecting portion decreases, resulting in a battery module with high operation voltage.
In this case, since the insulating ring is disposed around the outer periphery of the cylinder, the contact between the upper end part of the can of the one cell and the bottom of the can of the other cell can be securely prevented, resulting in a battery module causing no welding failure.
Further, the annular connecting member has a cylinder formed integrally with the sealing member and concentrically with a cap portion protruding from the sealing member, with an insulating ring disposed on an outside periphery of the cylinder, in which a lower end part of the cylinder is welded to the sealing member of the one cell, and an upper end part of the cylinder is welded to the bottom of the can of the other cell. Therefore, the collecting path has a height of the cylinder, whereby the voltage drop across the connecting portion decreases, resulting in a battery module with high operation voltage.
In this case, since the insulating ring is disposed around the outer periphery of the cylinder, the contact between the upper end part of the can of the one cell and the bottom of the can of the other cell can be securely prevented, resulting in a battery module causing no welding failure.
A method for manufacturing a battery module according to the present invention includes aligning a plurality of cells in one row by placing a connecting member having an aperture having a larger diameter than a cap at a position corresponding to the cap between a sealing member of one cell and a bottom of a can of the other cell, pressurizing the plurality of cells aligned in one row from both ends thereof at a predetermined pressure, and passing a welding current between a pair of welding electrodes disposed in contact with the metallic cans of arbitrary two adjacent cells, and welding the connecting member and the sealing member of the one cell, as well as the connecting member and the bottom of the can of the other cell.
In this way, since the plurality of cells are aligned in one row by interposing the connecting member having the aperture having larger diameter than the cap at the position corresponding to the cap, these cells are pressurized from both ends at a predetermined pressure, and a welding current is passed between a pair of welding electrodes disposed in contact with the metallic cans of arbitrary two adjacent cells, whereby a welding current flows from one of the pair of welding electrode through the bottom of the can of the one cell, the connecting member, the cap of the other cell, the inside of the other cell to the other of the pair of welding electrodes, or inversely.
Thereby, a Joule""s heat is produced in a contact part between the bottom of the can of the one cell and the connecting member, and a contact part between the cap of the other cell and the connecting member, causing these contact parts to be molten, and welded. As a result, the bottom of the can of the one cell and the cap of the other cell are welded together via the connecting member without using a positive electrode lead plate for the welding, whereby the voltage drop across the contact part decreases, resulting in a battery module with lower voltage drop having a number of cells connected in series.
Further the terminals of the same polarity in said adjacent cells can be connected with each other.